/*
 * Copyright (c) 2005, 2006, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package javax.lang.model.util;

import java.util.ArrayList;
import java.util.Collections;
import java.util.EnumSet;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Set;

import javax.lang.model.element.Element;
import javax.lang.model.element.ElementKind;
import javax.lang.model.element.ExecutableElement;
import javax.lang.model.element.PackageElement;
import javax.lang.model.element.TypeElement;
import javax.lang.model.element.VariableElement;

/**
 * Filters for selecting just the elements of interest from a collection of
 * elements. The returned sets and lists are new collections and do use the
 * argument as a backing store. The methods in this class do not make any
 * attempts to guard against concurrent modifications of the arguments. The
 * returned sets and lists are mutable but unsafe for concurrent access. A
 * returned set has the same iteration order as the argument set to a method.
 * 
 * <p>
 * If iterables and sets containing {@code null} are passed as arguments to
 * methods in this class, a {@code NullPointerException} will be thrown.
 * 
 * <p>
 * Note that a <i>static import</i> statement can make the text of calls to the
 * methods in this class more concise; for example:
 * 
 * <blockquote>
 * 
 * <pre>
 *     import static javax.lang.model.util.ElementFilter.*;
 *     ...
 *         {@code List<VariableElement>} fs = fieldsIn(someClass.getEnclosedElements());
 * </pre>
 * 
 * </blockquote>
 * 
 * @author Joseph D. Darcy
 * @author Scott Seligman
 * @author Peter von der Ah&eacute;
 * @author Martin Buchholz
 * @since 1.6
 */
public class ElementFilter {
	private ElementFilter() {
	} // Do not instantiate.

	private static Set<ElementKind> CONSTRUCTOR_KIND = Collections
			.unmodifiableSet(EnumSet.of(ElementKind.CONSTRUCTOR));

	private static Set<ElementKind> FIELD_KINDS = Collections
			.unmodifiableSet(EnumSet.of(ElementKind.FIELD,
					ElementKind.ENUM_CONSTANT));
	private static Set<ElementKind> METHOD_KIND = Collections
			.unmodifiableSet(EnumSet.of(ElementKind.METHOD));

	private static Set<ElementKind> PACKAGE_KIND = Collections
			.unmodifiableSet(EnumSet.of(ElementKind.PACKAGE));

	private static Set<ElementKind> TYPE_KINDS = Collections
			.unmodifiableSet(EnumSet.of(ElementKind.CLASS, ElementKind.ENUM,
					ElementKind.INTERFACE, ElementKind.ANNOTATION_TYPE));

	/**
	 * Returns a list of fields in {@code elements}.
	 * 
	 * @return a list of fields in {@code elements}
	 * @param elements
	 *            the elements to filter
	 */
	public static List<VariableElement> fieldsIn(
			Iterable<? extends Element> elements) {
		return listFilter(elements, FIELD_KINDS, VariableElement.class);
	}

	/**
	 * Returns a set of fields in {@code elements}.
	 * 
	 * @return a set of fields in {@code elements}
	 * @param elements
	 *            the elements to filter
	 */
	public static Set<VariableElement> fieldsIn(Set<? extends Element> elements) {
		return setFilter(elements, FIELD_KINDS, VariableElement.class);
	}

	/**
	 * Returns a list of constructors in {@code elements}.
	 * 
	 * @return a list of constructors in {@code elements}
	 * @param elements
	 *            the elements to filter
	 */
	public static List<ExecutableElement> constructorsIn(
			Iterable<? extends Element> elements) {
		return listFilter(elements, CONSTRUCTOR_KIND, ExecutableElement.class);
	}

	/**
	 * Returns a set of constructors in {@code elements}.
	 * 
	 * @return a set of constructors in {@code elements}
	 * @param elements
	 *            the elements to filter
	 */
	public static Set<ExecutableElement> constructorsIn(
			Set<? extends Element> elements) {
		return setFilter(elements, CONSTRUCTOR_KIND, ExecutableElement.class);
	}

	/**
	 * Returns a list of methods in {@code elements}.
	 * 
	 * @return a list of methods in {@code elements}
	 * @param elements
	 *            the elements to filter
	 */
	public static List<ExecutableElement> methodsIn(
			Iterable<? extends Element> elements) {
		return listFilter(elements, METHOD_KIND, ExecutableElement.class);
	}

	/**
	 * Returns a set of methods in {@code elements}.
	 * 
	 * @return a set of methods in {@code elements}
	 * @param elements
	 *            the elements to filter
	 */
	public static Set<ExecutableElement> methodsIn(
			Set<? extends Element> elements) {
		return setFilter(elements, METHOD_KIND, ExecutableElement.class);
	}

	/**
	 * Returns a list of types in {@code elements}.
	 * 
	 * @return a list of types in {@code elements}
	 * @param elements
	 *            the elements to filter
	 */
	public static List<TypeElement> typesIn(Iterable<? extends Element> elements) {
		return listFilter(elements, TYPE_KINDS, TypeElement.class);
	}

	/**
	 * Returns a set of types in {@code elements}.
	 * 
	 * @return a set of types in {@code elements}
	 * @param elements
	 *            the elements to filter
	 */
	public static Set<TypeElement> typesIn(Set<? extends Element> elements) {
		return setFilter(elements, TYPE_KINDS, TypeElement.class);
	}

	/**
	 * Returns a list of packages in {@code elements}.
	 * 
	 * @return a list of packages in {@code elements}
	 * @param elements
	 *            the elements to filter
	 */
	public static List<PackageElement> packagesIn(
			Iterable<? extends Element> elements) {
		return listFilter(elements, PACKAGE_KIND, PackageElement.class);
	}

	/**
	 * Returns a set of packages in {@code elements}.
	 * 
	 * @return a set of packages in {@code elements}
	 * @param elements
	 *            the elements to filter
	 */
	public static Set<PackageElement> packagesIn(Set<? extends Element> elements) {
		return setFilter(elements, PACKAGE_KIND, PackageElement.class);
	}

	// Assumes targetKinds and E are sensible.
	private static <E extends Element> List<E> listFilter(
			Iterable<? extends Element> elements, Set<ElementKind> targetKinds,
			Class<E> clazz) {
		List<E> list = new ArrayList<E>();
		for (Element e : elements) {
			if (targetKinds.contains(e.getKind()))
				list.add(clazz.cast(e));
		}
		return list;
	}

	// Assumes targetKinds and E are sensible.
	private static <E extends Element> Set<E> setFilter(
			Set<? extends Element> elements, Set<ElementKind> targetKinds,
			Class<E> clazz) {
		// Return set preserving iteration order of input set.
		Set<E> set = new LinkedHashSet<E>();
		for (Element e : elements) {
			if (targetKinds.contains(e.getKind()))
				set.add(clazz.cast(e));
		}
		return set;
	}
}
